Adaptive Cruise (i.e., speed) Control (ACC) systems operate much like conventional Cruise Control systems, with the added capability of being able to sense in-path vehicles and to slow the ACC equipped vehicle in response. An ACC equipped vehicle thereby allows its operator to automatically control the vehicle speed, as with conventional Cruise Control, without the necessity of having to deactivate and reactivate control whenever slower traffic is encountered.
As is well known in the art, existing ACC methods and systems use a forward looking range sensor such as radar to sense an in-path vehicle (which may also be referred to as a sensed target or primary target). Based on the radar sensor information, such ACC methods and systems then determine the range and relative velocity (or range rate) of the sensed in-path vehicle. Using the range and range rate, the speed of the ACC equipped vehicle is controlled to maintain a selected following interval between the ACC equipped vehicle and the sensed in-path vehicle. The speed of the ACC equipped vehicle is typically controlled by automatic control of the vehicle throttle actuator. In more advanced ACC methods and systems, vehicle speed may also be controlled by automatic control of vehicle brake actuators. Such ACC methods and systems have the ability to apply a moderate degree of braking to the vehicle to achieve further vehicle deceleration (i.e., in addition to vehicle deceleration achieved via throttle control) in response to an in-path vehicle.
Thus, in maintaining the selected following interval, existing ACC methods and systems may decelerate the ACC equipped vehicle. In such situations, the deceleration the ACC equipped vehicle may take any value up to a maximum allowed deceleration, which is typically 0.3 g. In existing ACC methods and systems, however, such a maximum allowed deceleration is constant, regardless of vehicle speed. As a result, at higher vehicle speeds, deceleration of the ACC equipped vehicle at the maximum allowed deceleration may be perceived as uncomfortable by the vehicle operator. Conversely, at lower vehicle speeds, deceleration of the ACC equipped vehicle at that same maximum allowed deceleration may be perceived as insufficient by the vehicle operator.
As a result, there exists a need in an ACC system for a method and system for controlling the maximum allowed vehicle deceleration based on the vehicle speed. More specifically, such a method and system would set the maximum allowed vehicle deceleration as a function of the vehicle speed, increasing the maximum allowed vehicle deceleration at lower vehicle speeds and decreasing the maximum allowed vehicle deceleration at higher vehicle speeds. Such a method and system would thereby provide the ACC equipped vehicle with a more comfortable response for the vehicle operator.